Recently, display technology develops rapidly. Thin film transistor serving as a switch component is evolving from an original amorphous silicon (a-Si) thin film transistor to current low-temperature polycrystalline silicon (LTPS) thin film transistor, metal-induced lateral crystallization (MILC) thin film transistor, Oxide thin film transistor and the like. Display device is evolving from original liquid crystal display (LCD) and plasma display panel (PDP) to current organic light-emitting diode (OLED) display, active matrix organic light-emitting diode (AMOLED) display and the like. The OLED display is a new generation of the display device; and compared with the liquid crystal display, the OLED display has many advantages such as self-luminescence, quick response, wide viewing angle, suitable for flexible display, suitable for transparent display, suitable for three-dimensional (3D) display and the like. However, both the liquid crystal display and the OLED display needs to equip each pixel with a switch for controlling the pixel, i.e., thin film transistor, such that a driving circuit independently controls each pixel without causing influences such as crosstalk on other pixels.
The oxide thin film transistor which is widely used adopts an oxide semiconductor as an active layer, has the characteristics of high mobility, high ON state current, better switching performance, better uniformity and the like, and is suitable for display device requiring quick response and large current, such as high-frequency, high-resolution and large-sized displays and organic light-emitting displays.
A fabrication process of the oxide thin film transistor generally requires six patterning processes to form a gate line and a gate electrode, a gate insulating layer, the active layer, an etching barrier layer, a source electrode and a drain electrode, a passivation layer and a via hole. However, the six patterning processes cause disadvantages such as instable performance, long fabrication cycle and increased fabrication cost.